Pressure gradient hydrophone



Nov. 21, 1967 F. MASSA 3,354,426

PRES SURE GRADIENT HYDROPHONE Filed Jan. 28, 1966 INVENTOR j FRANK MASSAATTORNEY United States Patent i 3,354,426 Patented Nov. 21, 1967 iceMass.

Filed Jan. 28, 1966, Ser. No. 523,780 11 Claims. (Cl. 340-10) Thisinvention is a continuation-in-part of my copending application SerialNo. 481,809, led August 23, 1965, which discloses a pressure gradienthydrophone that will operate satisfactorily throughout the lower portionof the audible frequency region. The novel design of that applicationalso provides for an equalization of the hydrostatic pressure before thepressure is transferred to the active transducer element so that thehydrophone is capable of operation when it is immersed in deep water.

This invention relates to pressure gradient transducers and moreparticularly to pressure gradient transducers usable as hydrophones tobe positioned underwater at relatively great depths. The transducers ofthis invention are relatively simple in construction and operation, arereadily and inexpensively manufacturable while being rugged and reliablein operation, with excellent response characteristics and sensitivity,particularly at extremely low frequencies.

The present invention achieves the same objects as set forth in theaforesaid copending application and has in addition the further objectof providing increased sensitivity at extremely low frequencies.

According to an important feature of the invention, connection means areprovided between diaphragm means which sealingly close opposite ends ofa generally tubular housing and an end portion of transducer meansmovable axially within the housing with the other end of the transducermeans being secured to an intermediate point in the housing. Preferably,the transducer means is in the form of a cantiliver beam. With thisarrangement, a very simple construction is provided with an equalizationof hydrostatic pressure such that the transducer can be immersed in deepwater, and increased sensitivity is obtained particularly at extremelylow frequencies.

In accordance with a specific feature of the invention, the movable endof the transducer means is positioned beyond a center line of thetubular housing and generally U-shaped yoke means are provided having abight portion secured to the movable end of the transducer means andhaving a pair of leg portions extending to the center line, with a pairof means extending along the center line connecting the leg portions tothe diaphragm means. Preferably, the transducer means has a lengthdimension which is substantially greater than the width dimensionthereof. With these features, a relatively long narrow transducer meansresults, to further increase sensitivity at extremely low frequencieswhile obtaining pressure equalization.

In accordance with further features of the invention, the transducermeans comprises a multilaminar plate assembly at least one element ofwhich comprises a transducer material capable of converting oscillatorymechanical stresses to alternating electrical signals. Preferably, atleast one plate of a polarized ceramic material is used.

In certain preferred embodiments of the invention, a pair of polarizedplates are used having faces of one polarity in facing relation. In oneof such embodiments, thin electrodes on the inward faces of theaforesaid one polarity are bonded together, while in another embodiment,a metallic plate is provided sandwiched between the transducer plates,having an inner end portion secured to an intermediate point of thehousing and having an opposite end portion mechanically coupled to thedia- A phragm means.

In another embodiment of the invention, the transducer means comprises asingle plate of piezoelectric material and a supporting plate bonded toone face of the plate of piezoelectric material.

This invention contemplates other objects, features and advantages whichwill become more fully apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings which illustratepreferred embodiments and in which:

FIGURE l is a longitudinal sectional view of one preferred embodiment ofa pressure gradient hydrophone constructed according to the principlesof this invention;

FIGURE 2 is a sectional view taken substantially along line II-II ofFIGURE 1;

FIGURE 3 is a plan view of a modied form of transducer assembly usablein place of that shown in FIG- URE 1;

FIGURE 4 is a sectional view taken substantially along line VI-VI ofFIGURE 3; and

FIGURE 5 is a sectionalview similar to FIGURE 4, but illustratinganother modified form of transducer assembly according to the invention.

Referring to FIGURE 1, reference numeral 10 generally designates apressure gradient hydrophone constructed in accordance with theprinciples of this invention. The hydrophone 10 comprises transducermeans 11 disposed within a generally tubular housing structure which isgenerally designated by reference numeral 12, with vibratile diaphragmmeans 13 and 14 sealingly closing opposite ends of the tubular housingstructure 12 and mechanically coupled to the transducer means 11, bymeans including a pair of rods 15 and 16 extending along the centralaxis of the housing means 12. l

The transducer means 11 comprises two plates 17 and 18 of piezoelectricmaterial, preferably polarized barium titanate or polarized leadzirconate titanate which are bonded together, with one end. of theassembly being cemented against both an internal annular shoulder 19 andan internal generally cylindrical surface 20,of .a ring 21 forming anintermediate part of the housin structure 12.

The other end of the transducer assembly 11 is movable axially withinthe housing structure 12 and is mechanically coupled to the diaphragmmeans 13 and 14'through the rods 15 and 16. Preferably, and inaccordance with an important feature of the invention, the mechanicalcoupling means comprises a generally U-shaped yoke 23 having a bightportion 24 cemented to the movable end of the transducer assembly, andhaving leg portions 25 and 26 extending to the center line of thehousing structure 12 and having openings for receiving reduced diameterpin portions 27 and 28 at the ends of the rods 15 and 16. With thisarrangement, the movable end of the transducer assembly 11 extends Wellbeyond the cenvter line of the housing structure 12 and, as shown inFIGURE 2, the width of the transducer assembly is less than the lengththereof, these features cooperating to increase the sensitivity of thehydrophone at extremely low frequencies.

As indicated by the plus and minus signs in FIGURE 1, the inner facingsurfaces of the polarized transducer plates 17 and 18 are of the samepolarity (a negative polarity as indicated on the drawing), and thinelectrodes 29 and 30 formed on such inner facesare bonded together.Electrodes 31 and 32 are provided on the outer faces of the transducerplates 17 and 18, which are also of the same polarity (a positivepolarity as indicated on the drawing), and such electrodes 31 and 32 areconnected to wires 33 and 34 extending through insulated bushings 35 and36 in the wall of the ring 21.

The wires 33 and 34 form terminal means for connection of the hydrophone-to a suitable amplifier. With the described polarization of thetransducer plates 17 and 18, the combined series voltages across bothplates are additive when the movable end of the transducer assembly isdeflected in response to movements of the diaphragm means 13 and 14.

In addition to the intermediate ring 21, the housing structure 12comprises a pair of tubular members 37 and 38 with an inner end portion39 of member 37 being tightly fitted on a reduced diameter portion 40 atone end of the ring 21 and with a reduced diameter portion 41 at theinner end of member 38 being fitted within the other end of the ring 21.

The diaphragm means 13 and 14 are in the form of circular end plates orcaps disposed tightly against the end of the tubular members 37 and 38and having annular grooves on the inside surfaces thereof to definerelatively thin webs 43 and 44 which provide a exural suspension forcentral piston portions 45 and 46 connected to the ends of the rods and16, the rods 15 and 16 preferably having reduced diameter end portions47 and 48 extending into openings in the center of the piston portions45 and 46.

An epoxy cement is preferably employed at each joint where themechanical parts are attached together, to make a permanent, rigid,waterproof bond.

Referring to FIGURES 3 and 4, reference numeral 50 generally designatesa modied transducer and yoke assembly which may be substituted for thetransducer means 11 and the yoke 23 of the hydrophone of FIGURE 1. Inthe assembly 50, a piezoelectric plate 51 is provided, which maypreferably ybe polarized barium titanate or polarized lead zirconatetitanate, for example. The plate 51 has an electrode 52 on one facethereof and a pair of separate electrodes 53 and 54 on the other facethereof, a longitudinally extending relatively narrow gap being providedbetween the electrodes 53 and 54 to which leads 55 and 56 are secured.The plate 51 is bonded to a plate 58 which may be of aluminum or someother suitable material, preferably |by means of a rigid cement such asepoxy which preferably also serves to insulate the electrode 52 from thesurface of the plate 58. The plate 5S has an vend portion adapted to becemented or otherwise secured to the shoulder 19 and surface 20 of thering 21 and an opposite movable end portion 60 which is disposed betweenlegs of a pair of L-shaped members 61 and 62 to form a yoke, with arivet 63 extending through the legs of the members 61 and 62 and theportion 60. The other legs of the L-shaped members 61 and 62 haveopenings 65 and 66 for receiving the reduced diameter portions 27 and 28of the rods 15 and 16.

The plate 51 may be polarized =by applying a positive voltage onelectrode 53 and a negative voltage on electrode 54 with a center tapfrom the polarizing voltage being connected to the electrode 52 on theopposite side of the plate 51, the plate 51 being cemented on the plateV58 after polarization. When the assembly 50 is then installed in placeof the transducer means 11 and yoke 23 in the arrangement of FIGURE 1,an alternating force acting on the diaphragms 13 and 14 will set up avibra- -tion of the end 60 of the plate 58 and alternating additivevoltages will be generated across the sections to which electrodes 53and 54 are attached, to develop an AC signal between the conductors 55and 56.

Referring now to FIGURE 5, reference numeral 68 generally designatesanother form of transducer and yoke assembly which may be substitutedfor the transducer means 11 and yoke 23 of the arrangement of FIGURE 1.In theassembly 68, a plate 70 of aluminum or some other suitablematerial is provided, similar to the plate 58 of the assembly 50 ofFIGURES 3 and 4, and having an end 7,1 adapted to be cemented orotherwise secured to the shoulder 19 and internal surface 20 of the ring21 and having an opposite movable end 72 disposed between the legs oftwo L-shaped members 73 and 74 with a rivet `7,5 extendihg through legsof the members 73 and 74 and the end portion 72 of the plate 70, andwith openings 77 and 78 in the other legs of the members 73 and 74 forreceiving the reduced diameter portions 27 and 28 of the the rods 15 and16. In this arrangement, an intermediate portion of the plate 70 issandwiched between two transducer plates 79 and 80 having polarizationssimilar to the polarizations indicated in FIGURE 1. Electrodes 81 and 82on the outer surfaces of the plates 79 and 80 are connected toconductors 83 and 84, while electrodes 85 and 86 on the inside surfacesof the plates 79 and 80 are cemented to the plate 70, preferably bymeans of an epoxy cement, and preferably with the cement serving toelectrically insulate the electrodes 85 and 86 from the oppositesurfaces of the plate 70.

The illustrated ararngements operate in a manner similar to thosedisclosed in my copending application Serial No. 481,809, filed August23, 1965. The basic difference in result is that the arrangements ofthis application are particularly adapted for increased sensitivity atextremely low frequencies. When operation of the pressure gradienthydrophone is desired at the lowest portion of the audible frequencyrange and where high frequency operation is not essential, the increasedsensitivity can be obtained with the arrangements disclosed in thisapplication. The hydrophone will have maximum sensitivity for soundarriving along an axis parallel to the normal axis of the cylindricalstructure. For any sound arriving along the path which at right anglesto the axis of the hydrophone, the instantaneous sound pressure will beof the same magnitude and phase on the surface of each diaphragm, and,therefore, 0 voltage will be generated by the hydrophone. For soundarriving at angles |between 0 and 90, the sensitivity will beproportional to the cosine of the angle which the axis of the soundsource makes with the axis of the hydrophone.

Although I have chosen only a few examples to illustrate the basicprinciples of my invention, it will be 0bvious to those skilled in theart that numerous departures may be made from the details shown, and I,therefore, desire that my invention shall not be limited except insofaras is made necessary by the prior art and by the `Spirit of the appendedclaims.

I claim as my invention:

1. In combination in a pressure gradient transducer, generally tubularhousing means, end plates on opposite ends of said housing means havingannular grooves therein defining relatively thin webs for liexuralsuspension of central piston portions thereof, transducer meanscomprising a multilaminar plate assembly with at least one element ofsaid plate assembly comprising a transducer material capable ofconverting oscillatory mechanical bending stresses to alternatingelectrical signals, means for rigidly supporting one end of saidmultilaminar plate assembly at a point within said housing meansintermediate said end plates to position the opposite end of saidassembly beyond a center line of said tubular housing means, U-shapedyoke means having a bight portion secured to said opposite end of saidassembly and having a pair of leg portions extending to said centerline, a pair of rigid rods extending along said center line and rigidlyconnected to said central piston portions of said end plates and to saidleg portions of said yoke means, and electrical terminal means forconnecting said transducer material to an external circuit.

2. In combination in a pressure gradient transducer, generally tubularhousing means, vibratile diaphragm means sealingly closing opposite endsof said housing means, a somewhat elongated transducer means having twoend portions, said transducer being sealed within said housing means,one of said end portions being secured to a point in said housing meansintermediae said opposite ends, the opposite end portion being free tomove axially in said elongated dimension within said housing means, andconnection means extending through said housing and rigidly attachedbetween the diaphragm means fpr mechanically coupling said opposite endportion to said diaphragm means.

3. In a pressure gradient transducer as defined in claim 2, saidtransducer means being in the form of a cantilever beam.

4. In a pressure gradient transducer as defined in claim 2, saidtransducer means comprising a multilaminar plate assembly with at leastone elementl of said plate assembly comprising a transducer materialcapable of converting oscillatory mechanical stresses to alternatingelectrical signals, and electrical terminal means connected to saidtransducer material.

5. In a pressure gradient transducer as defined in claim 2, saidtransducer means having a length dimension as measured in a directionbetween said one end and said opposite end which is many times greaterthan a width dimension as measured in a direction transverse to saidlength direction.

6. In a pressure gradient transducer as defined in claim 2, saidtransducer means comprising a plate of a polarized ceramic material.

7. In a pressure gradient transducer as deined in claim 2, saidtransducer means comprising a pair of plates of polarized ceramicmaterial having faces of one polarity in facing relation, electrodemeans on said faces of said one polarity, electrodes on the oppositefaces of said plates, and electrical terminal means connected to saidelectrodes on said opposite faces of said plates.

8. In a pressure gradient transducer as defined in claim 7, saidelectrodes on said faces of said one polarity being directly bondedtogether.

9. In a pressure gradient transducer as dened in claim 7, a supportingplate sandwiched between said faces of said plates of said one polarityand having one end portion secured to said intermediate point in saidhousing means and an opposite end portion defining said opposite endportion which is mechanically coupled to said diaphragm means.

10. In combination in a pressure gradient transducer, generally tubularhousing means, vibratile diaphragm means sealingly closing opposite endsof said housing means, transducer means within said housing means havingone end portion secured to a point in said housing means intermediatesaid opposite ends and having an opposite end portion movable axiallywithin said housing means, said transducer means comprising amultilaminar plate assembly with at least one element of said plateassembly comprising a transducer material capable of convertingoscillatory mechanical stresses to alternating electrical signals,electrical terminal means connected to said transducer material,connection means mechanically coupling said opposite end portion to saiddiaphragm means, said opposite end portion of said transducer meansbeing positioned beyond a center line of said tubular housing means, andsaid connection means comprising generally U-shaped yoke means having abight portion secured to said opposite end of said transducer means andhaving a pair of leg portions extending to said center line and a pairof means extending along said center line connecting said leg portionsto said diaphragm means.

11. In combination in a pressure gradient transducer, generally tubularhousing means, vibratile diaphragm means sealingly closing opposite endsof said housing means, transducer means within said housing means havingone end portion secured to a point in said housing means intermediatesaid opposite ends and having an opposite end portion movable axiallyWithin said housing means, connection means mechanically coupling saidopposite end portion to said diaphragm means, said transducer meansdefining a plate lof piezoelectric material and a supporting platebonded to one face of said plate of piezoelectric material and havingone end portion secured to said intermediate point in said housing meansand an opposite end portion defining said opposite end portion which ismechanically coupled to said diaphragm means, a pair of electrodes onseparate portions of the opposite face of said plate of piezoelectricmaterial, said piezoelectric material being a polarized ceramic materialwith the portions on which said pair of electrodes are attached beingoppositely polarized, and terminal means connected to said pair ofelectrodes.

References Cited UNITED STATES PATENTS 2,497,672 2/ 1950 Jaffe.2,647,162 7/ 1953 Duncan. 2,659,829 11/1953 Baerwald 340-10 X RODNEY D.BENNETT, Primary Examiner. CHESTER L. JUSTUS, Examiner B. L. RIBANDO,Assistant Examiner.

1. IN COMBINATION IN A PRESSURE GRADIENT TRANSDUCER, GENERALLY TUBULARHOUSING MEANS, END PLATES ON OPPOSITE ENDS OF SAID HOUSING MEANS HAVINGGROOVES THEREIN DEFINING RELATIVELY THIN WEBS FOR FLEXURAL SUSPENSION OFCENTRAL PISTON PORTIONS THEREOF, TRANSDUCER MEANS CONPRISING AMULTILAMINAR PLATE ASSEMBLY WITH AT LEAST ONE ELEMENT OF SAID PLATEASSEMBLY COMPRISING A TRANSDUCER MATERIAL CAPABLE OF CONVERTINGOSCILLATORY MECHANICAL BENDING STRESSES TO ALTERNATING ELECTRICALSIGNALS, MEANS FOR RIGIDLY SUPPORTING ONE END OF SAID MULTILAMINAR PLATEASSEMBLY AT A POINT WITHIN SAID HOUSING MEANS INTERMEDIATE SAID ENDPLATES TO POSITION THE OPPOSITE END OF SAID AS-